The invention relates to a semiconductor device with a semiconductor body comprising a substrate and a first semiconductor region which lies in the semiconductor body, which is of a first conductivity type, which forms a collector region of a bipolar transistor, which is provided with a first connection conductor, and above which a second semiconductor region of a second conductivity type opposed to the first is present, forming a base region of the transistor, adjoining the surface of the semiconductor body, and being provided at said surface with a second connection conductor, and a third semiconductor region which lies recessed in the second semiconductor region, which is of the first conductivity type, which forms an emitter region of the transistor, and which is provided with a third connection conductor, said device being provided with means for limiting the degree of saturation of the transistor during normal use. The invention also relates to a method of manufacturing such a device.
Such a device with a bipolar transistor is frequently used as a switching transistor, for example in a static power conversion circuit. The switching speed of the transistor, which is usually a discrete component, should often be as high as possible.
Such a device and method are known from U.S. Pat. No. 4,969,027 published on Nov. 6th, 1990. A bipolar transistor is disclosed therein (see FIG. 1B) which is provided with means for limiting the saturation. Said means comprise a Schottky clamping diode integrated into the device and formed in that the connection conductor of the base region is also put into contact with the collector region. Since the Schottky diode limits the degree of saturation, the switching time of the transistor is as short as possible, while on the other hand the latter does not get very far removed from the saturated state, which implies that a high collector-emitter voltage and high losses in the on-state are avoided.
A disadvantage of the known device is that it is less suitable for mass manufacture. Such a manufacture renders it important that the properties of the device within a batch and among batches do not vary too widely. The leakage current of a Schottky diode, however, is often too variable, in particular at higher temperatures. This is because the surface of the semiconductor body has a major influence on said leakage current, and because the properties of a surface are often difficult to control. A further influence here is the occurrence of so-called spikes, i.e. locations where the metal of the connection conductor of the base region penetrates into the collector region.